1. Field of the Invention
The present invention relates to a rotation sensor for sensing rotation of an input shaft or an output shaft of an automatic transmission of a vehicle or the like. Specifically, the present invention relates to a rotation sensor for sensing the rotation by sensing an angular change of a magnetic vector.
2. Description of Related Art
An automatic transmission, for example, as shown in FIG. 10, automates clutch operation or gear-changing and is mounted on a vehicle. As shown in FIG. 10, the automatic transmission has a torque converter 110 and an automatic transmission mechanism 120. The torque converter 110 is driven by an engine and converts torque of the engine. The automatic transmission mechanism 120 automatically adjusts a rotation ratio, i.e., a gear ratio, between an input shaft 121, which is rotated by the torque transmitted through the torque converter 110, and an output shaft 122 mounted on an opposite side from the input shaft 121.
The torque converter 110 receives the torque (rotational force) of a crankshaft CSH, i.e., output shaft, of the engine and stably transmits the rotational force to the automatic transmission mechanism 120. The torque converter 110 also has a function of increasing the rotational force of the crankshaft CSH when the motive power of the engine increases and the rotation speed of the crankshaft CSH increases.
The automatic transmission mechanism 120 has a gear portion, a clutch, an oil pressure circuit, and an electronic controller. The gear portion includes a planetary gear mechanism that variably controls the gear ratio between the input shaft 121 and the output shaft 122. The clutch turns on or off the variable control performed by the gear portion for varying the gear ratio. The oil pressure circuit and the electronic controller control the on-off operation of the clutch.
Thus, the motive power of the engine is transmitted to the input shaft 121 of the automatic transmission mechanism 120 through the torque converter 110, and the input shaft 121 starts rotating at a predetermined rotation speed. The electronic controller of the automatic transmission mechanism 120 automatically controls the on-off operation of the clutch and the variable control of the gear ratio performed by the gear portion, based on conditions such as vehicle speed and engine rotation speed, which are input every time the automatic control is performed. Thus, the output shaft 122 rotates at a suitable gear ratio with respect to the input shaft 121.
A rotation sensor is typically mounted to the input shaft 121 or the output shaft 122 of the automatic transmission to monitor rotation speed of the input shaft 121 or the output shaft 122. Thus, the suitability of the gear change control can be examined.
If the rotation sensor is mounted in the automatic transmission, i.e., if the rotation sensor is mounted to the input shaft 121 or the output shaft 122 of the automatic transmission mechanism 120, usually, a spur gear rotor made of a magnetic material is mounted to the input shaft 121 or the output shaft 122. A rotation sensor that has a sensor and a bias magnet is located near the rotor. The sensor has a magnetic resistance element. The bias magnet applies a bias magnetic field to the magnetic resistance element. The rotation sensor senses rotation characteristics of the rotor such as speed by sensing a change in a magnetic vector, which is generated by the rotation of the rotor and by the bias magnetic field, as a change of a resistance of the magnetic resistance element. However, if the rotation sensor is mounted in such a way, space inside the automatic transmission is occupied by the rotor. In an extreme case, there is a possibility that a design of the automatic transmission itself has to be changed to accommodate the rotor.